JPH0569424A - Cast molding of ceramic - Google Patents

Abstract

PURPOSE:To prevent a rise in the viscosity of a ceramics powder slurry to which an acrylic emulsion is added as a binder at the time of the cast molding of said slurry. CONSTITUTION:An acrylic emulsion is added to and mixed with a ceramics powder slurry under stirring in a vacuum defoaming process before cast molding. By this method, the breakdown of the emulsion due to mill mixing is prevented and a rise in the viscosity of the ceramics powder slurry is not generated and no crack is generated in a cast molded product. Further, a binder mixing process is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramics casting method, and more particularly to a ceramics casting method using a ceramic powder slurry to which an acrylic emulsion is added as a binder.

[0002]

2. Description of the Related Art The cast molding method can produce a ceramic molded body having a complicated shape. Therefore, it is very useful for producing a ceramic product such as a gas turbine component which cannot be molded by using a press. This is a useful molding method.

Conventionally, polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) have been used as the binder of the ceramic powder slurry, but these are water-soluble binders, and the slurry using the water-soluble binder is cast. When applied to the molding method, there is a problem that when water is absorbed in the gypsum mold, the binder also migrates, the gypsum mold is clogged, and the gypsum mold cannot be reused.

In particular, since non-oxide ceramics are sintered in a non-oxidizing atmosphere such as nitrogen or argon,
In the case of a non-volatile binder, especially CMC, there is a problem that ash content due to incomplete combustion remains, which adversely affects the characteristics of the sintered body.

For the above reasons, acrylic emulsion is often used as a binder for ceramics slurry for casting.

[0006]

However, when an acrylic emulsion is added as a binder during the preparation of the slurry, the emulsion is destroyed during the slurry mixing,
There was a problem that the viscosity of the slurry was increased, resulting in cracks and insufficient filling of the molded body. Therefore, it has been practiced to add only the acrylic emulsion afterwards and mix it for a short time with a mill. However, in this case, not only the step of adding the binder was increased, but also the emulsion was broken due to the rapid mixing by the mill, and it was difficult to control the binder mixing time.

[0007]

Therefore, the present inventors have conducted various studies on a suitable binder addition method for producing a ceramics slurry suitable for cast molding, and as a result, the vacuum of the slurry during the cast molding process has been found. The above problem was solved by adding and mixing a binder during defoaming.

That is, the present invention is a cast molding method using a ceramic powder slurry to which an acrylic emulsion is added as a binder, wherein the binder is mixed by stirring in a vacuum degassing tank. Is.

When the slurry is poured into the mold in cast molding, if the slurry contains air bubbles, the air bubbles will not disappear until after the sintering, and the strength of the ceramics sintered body will be reduced as a starting point of destruction. To do. Therefore, a step of defoaming the bubbles contained in the slurry by a defoaming device is required before pouring the slurry into the mold by casting.

Generally, a defoaming device for a slurry encloses the slurry in a container capable of depressurizing, lowers the pressure inside the container, and stirs the slurry by a stirring device such as a propeller arranged in the container. Then defoam.

In the present invention, a binder is added in this defoaming step, and stirring and mixing are carried out by a propeller arranged in the container. This prevents the emulsion from being broken in the mill mixing and the binder mixing step. Can be simplified.

In the present invention, the stirring and mixing time of the binder in the vacuum foaming tank is preferably 1 to 10 hours,
If it is less than time, a sufficient mixing effect cannot be obtained, while if it exceeds 10 hours, the emulsion is broken and the viscosity increases, which is not preferable.

The amount of the binder added is preferably 1 to 10 parts by weight as the binder weight in the acrylic emulsion with respect to 100 parts by weight of the ceramic powder in the slurry. If it is less than 1 part by weight, sufficient strength cannot be obtained.
If it exceeds the weight part, the time required for debinding will be long, and cracks may occur in the molded product during debinding.

The acrylic emulsion used as a binder in the present invention is a commercially available binder for cast molding of ceramics, such as WA-320 manufactured by Mitsui Toatsu Co., Ltd.

The degree of polymerization of acrylic emulsion is 50,000 to 10
0,000 is preferable. If it is less than 50,000, sufficient strength cannot be obtained,
On the other hand, if it is 1,000,000 or more, the viscosity of the slurry increases, resulting in cracks or insufficient filling of the molded body, which is not preferable.

The ceramic powder in the present invention includes alumina, zirconia, silicon carbide, silicon nitride,
Although there are sialon and the like, these ceramic powders are the main components, and other materials may be contained for improving the characteristics, which are also included in the present invention. Other materials include ceramic whiskers and carbon fibers.

As a method for preparing the ceramic powder-containing slurry, a conventional method can be followed. For example, in the case of Sialon powder, 40 parts by weight of a solvent (water, organic solvent, etc.) and 0.1-2.0 parts by weight of a deflocculant are added to 100 parts by weight of Sialon powder having an average particle size of 0.2 to 1.0 μm and mixed by a mill. To create a slurry.

As the above-mentioned solvent, water, an organic solvent or the like is used, and a mixed solvent can also be used. Examples of the organic solvent used include methanol, ethanol, isopropyl alcohol, xylene, and hexane.

The viscosity of the casting slurry used in the present invention is 10 poise or less as a standard, and it is preferably 5 poise or less.

The cast molding method using the slurry and the firing method of the molded body can be carried out by conventional methods.
For example, as the casting molding method, each means such as sludge casting, solid casting, pressure casting, vacuum casting and the like can be mentioned. On the other hand, as the sintering method of the obtained molded body, an atmospheric sintering method,
Gas pressure sintering, HP, HIP, etc.

[0021]

In the present invention, as described above, the acrylic emulsion is added as a binder at the time of vacuum defoaming of the slurry immediately before the casting and molding step, and the mixture is stirred and mixed, so that the emulsion is not broken and the viscosity is increased by the conventional mill mixing. At the same time, the binder mixing process is simplified.

[0022]

Example 1 Sialon Si _5.5 Al _0.5 O _0.5 N _7.5 (Z = having an average particle size of 0.5 μm)
0.5 parts by weight of the powder of 0.5) and 40 parts by weight of ion-exchanged water are put in a resin ball mill, and 0.5 parts by weight of polyoxyethylene alkylphenyl ether and ammonium polycarboxylate as peptizers are added thereto and mixed for 18 hours. To make a slurry.

An acrylic emulsion having a polymerization degree of 400,000 (WA manufactured by Mitsui Toatsu Co., Ltd.) was used as a binder in the obtained slurry.
-320) was added in an amount of 8 parts by weight in terms of solid content, and the mixture was stirred and mixed in a vacuum degassing tank for 2 hours, and then the degassing tank was evacuated for another 2 hours to degas the slurry. The viscosity of the obtained slurry was 0.8 poise.

Immediately add this slurry to 150 × 150 × 20 mm
Perform plaster molding with a plaster mold of 3 and apply a molding pressure of ² kg / cm ² for 3
After leaving it for a while to solidify, remove the gypsum mold and leave the molded body at 20 ° C.
And dried for 3 days. The obtained molded product had a sufficient bending strength and there was no problem in its handling.

The obtained molded body is put into a sintering furnace and heated at 450 ° C.
After degreasing for 3 hours, the temperature was raised to 1700 ° C. and sintering was performed for 3 hours to obtain a sintered body having a density of 3.2 g / cm ³ . No cracks were observed due to the degreasing treatment and the sintering treatment.

Example 2, Comparative Examples 1 to 5 Sintered bodies were obtained in the same manner as in Example 1 except that acrylic emulsions having the degrees of polymerization shown in Table 1 were stirred and mixed in the amounts and mixing times shown in Table 1, respectively. It was

Table 1 shows the viscosity of the slurry after mixing the binder, the bending strength of the dried molded product, and the presence or absence of cracks in the sintered product together with the results of Example 1.

[0028]

[Table 1]

Comparative Example 6 With the same formulation as in Example 2, a binder was added into the mill when the slurry was prepared and mixed for 15 hours. The viscosity of the obtained slurry reached 120 poise, and cast molding could not be performed.

[0030]

As described above, according to the present invention, an acrylic emulsion is added as a binder at the time of defoaming the slurry, and the binder is mixed by stirring and mixing in a vacuum defoaming tank so that the emulsion is not destroyed by mill mixing. In addition, since the binder mixing step can be simplified, it is possible to easily manufacture a sialon molded product having a complicated shape that cannot be molded by press molding and a sintered body thereof without cracks.

Claims (2)

[Claims] 1. A cast molding method for ceramics, characterized in that, in a cast molding method using a ceramic powder slurry to which an acrylic emulsion is added as a binder, the binder is mixed by stirring in a vacuum degassing tank. 2. Acrylic emulsion having a degree of polymerization of 50,000 to
The method according to claim 1, wherein the stirring time in the vacuum degassing tank is 1 to 10 hours at 1 million.